The present invention relates to the drilling of bores in jaw bone tissue in preparation for the insertion of dental anchors.
One technique for the installation of dental prostheses involves drilling a bore into a patient's jaw bone and the insertion of a dental anchor into the bore. The bore is formed with a core of bone on the floor of the bore which fits into a recess in the front end of the anchor. Eventually, bone tissue grows against the anchor to fixedly secure the anchor in place. Techniques of this type are disclosed in U.S. Pat. No. 4,431,416 and copending U.S. application Serial Nos. 06/896,101 and 06/896,524 filed Aug. 13, 1986.
The bore, which is drilled in such fashion as to leave a center core therein, is drilled in three stages. In the first stage, a pilot hole is made by a drill bit. Then, within the pilot hole is installed a guide bushing which comprises two cylinders attached end-to-end. One of the cylinders is of small diameter and is inserted into the pilot hole. The drill head of a trephine drill is inserted over the large diameter cylinder in telescoping fashion and is advanced into the bone tissue during a second stage of the operation. The large diameter cylinder acts as a guide for the trephine drill to prevent the latter from moving sideways. The drill is advanced to a depth short of the final depth and, when removed, leaves a center core of bone. A hand tool is then inserted into the bore in order to break-off the core. Then, during the final step, the drill is reinserted into the bore and advanced to a final depth.
It is necessary that the bore be made sufficiently deep to receive the anchor, but not so deep that a nerve may be cut and damaged. This requires a certain drilling precision which, to date, has been difficult to achieve.
At present, it is conventional to employ a trephine drill which has markings on its side to indicate the depth attained by the drill. However, it is difficult for an operator to accurately see the markings during a drilling procedure, requiring the operator to repeatedly interrupt the drilling procedure to check the marks. Such a practice is time-consuming and does not guarantee that the required depth will not be exceeded.
It has been proposed in Swiss Pat. No. 302,233 to terminate the advancement of a drill by means of a stop adjustably fixed on the drill. However, i is difficult and time-consuming to adjust the stop to a precise position on the drill. Also, since the stop is fixed by a set screw, it is possible that if the set screw becomes inadvertently loosened, allowing the stop to move, severe damage can result from excessive advancement into the jaw bone.
It would be desirable to provide drilling apparatus and methods which enable a bore to be drilled quickly to the desired depth, with absolutely no chance whatsoever that the desired depth could be exceeded to any appreciable extent.